U.S. Pat. No. 5,919,044 discloses a flexible dental post comprising a bundle of optical fibers that are uniformly directed and twisted in a non-axial arrangement in order to impart additional strength to the dental post. The fiber bundle is embedded in a resin binder and extends from the apical end to the coronal end of the post. In this way, light can be guided in between the two end points of the post. In addition, a transverse light conduction towards the circumferential surface of the post can be achieved by etching or scoring the coating of the fibers yielding several light leakage points along the course of each fiber. The light escaping from these leakage points, however, must pass through the resin binder surrounding the fibers in order to arrive at the circumferential surface of the post. Thus, the choice of material for the resin matrix depends on its good light conduction properties and favorable materials with low transparency may not be applicable.
U.S. Pat. No. 5,989,032 discloses a dental post with a central axis comprising optical fibers embedded in a transparent resin matrix, wherein no particular direction of the fibers is favored. The dental post can be complemented by a truncated cone shaped prostethic structure which may be a separate piece or formed as an integral part attached to the post. In addition, a setting product for fixing the dental post and the prostethic core on a tooth stump is disclosed. In order to be transparent to visible light, the setting product may comprise randomly distributed short optical fibers or long optical fibers wound around stiffening elements. Thus, a polymerization of the setting product can be achieved by projecting visible light either directly on the setting product or on the transparent dental post. In the latter case of light being applied on the dental post, a transparent resin material is used for allowing the light conduction within the post. This, however, restricts the choice of available materials for the resin matrix.
Patent application no. DE 38 25 601 relates to a dental device consisting of an apical portion constituting a dental post to be inserted into a tooth stump and a truncated cone shaped coronary portion constituting a prosthetic structure to be arranged on top of the tooth stump. The dental device comprises optical fibers extending from the apical end to the coronary end of the dental post and continuing towards the end surface of the coronary prosthetic structure. Thus, light conduction through the fibers is only possible between the two end points of the dental device and no light can be extracted from the lateral surface of the dental post.
Patent application no. FR 2 874 498 describes a dental post consisting of fiber-reinforced material, wherein fibers and X-ray absorbing particles are embedded in a composite resin matrix. An advantage of the glass or carbon fibers located within the matrix lies in an improvement of the mechanical properties of the post leading to a similar modulus of elasticity as compared to that of the dentine. Besides the mechanical performance of the composites, a high degree of radiopacity and of translucency are important factors to be considered in the design of such a device. In this regard, above cited reference proposes to include X-ray absorbing particles with a size in between 95 nm and 200 nm in the resin matrix in order to allow the resin material to be translucent to light rays with a respective wavelength. Thus, a certain degree of light conduction is ensured within the resin matrix in order to allow light transmission across the interior of said dental post. Furthermore, the described post comprises a tapered structure running with a constant slope in the longitudinal direction and facilitating fitting inside the cavity formed by a tooth root canal.
A disadvantage of this dental post is that no retention means are provided in order to secure the position of the post within the root canal. A further drawback of this dental post is that the exploitation of the resin matrix as a light conductor not only restricts the choice of a preferred X-ray absorbing material in order to avoid the scattering of light rays, but also leads more generally to a certain loss that is related to light diffusion occurring in the resin matrix.
Patent application no. FR 2 882 646 discloses a dental post comprising a conical end portion and a threaded intermediate portion. The advantage of the threaded portion is an improved mechanical retention of the post within the tooth root canal e.g. for preventing an axial or rotational displacement of the post. The proposed slope and shape of the thread is mainly adapted to the intermediate cylindrical surface of the post and does not extend over its conical end portion at which the disposal of such a thread may induce an undesired breaking point. Furthermore, the narrow spacing between adjacent circumferential cycles of the single thread may lead to a large rate of scattering or diffusion of light if applied to a light conducting dental post.